Lithographic method

A method of measuring pellicle deflection in a lithographic apparatus, the method comprising:

• causing scanning movements of a sensing system assembly in the lithographic apparatus, the sensing system assembly comprising a two-dimensional array of pressure sensors supported by a support structure and further comprising a pellicle frame and a pellicle, wherein the two-dimensional array of pressure sensors is located between the support structure and the pellicle and configured to measure pressure changes caused by movements of the pellicle, wherein the support structure is not a conventional mask, and wherein the sensing system assembly has outer dimensions which correspond with outer dimensions of a mask assembly comprising a conventional mask, pellicle frame and pellicle;
• obtaining pressure measurements using the sensing system assembly;
• and
• calculating deflections of the sensing system assembly pellicle that occur during the scanning movements.

A method for a scanning exposure of a target portion of a substrate using a lithographic apparatus, the scanning exposure involving passing a radiation beam through a mask and through a pellicle of the mask during scanning movement of the mask and associated pellicle along a scanning direction and during scanning movement of the substrate and using a projection system of the lithographic apparatus to expose the target portion of the substrate with the radiation beam, the method comprising:

• obtaining pressure information from a plurality of pressure measurements near the pellicle along the scanning direction;
• and
• applying an adjustment to one or more lenses of the projection system for the scanning movement,
• wherein the adjustment takes into account pressure variations in an environment between the projection system and the pellicle caused by scanning movement of the mask and pellicle and determined from at least the pressure information, and
• wherein the adjustment compensates for aberrations due to deformation of the pellicle caused by the pressure variations.

A non-transitory computer program product comprising computer readable instructions therein, that when executed, are configured to cause a computer system to at least:

• obtain pressure information from a plurality of pressure measurements near a pellicle of a mask along a scanning direction, wherein a scanning exposure of a target portion of a substrate using a lithographic apparatus involves passing a radiation beam through the mask and through the pellicle during scanning movement of the mask and associated pellicle along the scanning direction and during scanning movement of the substrate and using a projection system of the lithographic apparatus to expose the target portion of the substrate with the radiation beam;
• and
• determine an adjustment to one or more lenses of the projection system for the scanning movement,
• wherein the adjustment takes into account pressure variations in an environment between the projection system and the pellicle caused by scanning movement of the mask and pellicle and determined from at least the pressure information, and
• wherein the adjustment compensates for aberrations due to deformation of the pellicle caused by the pressure variations.